Animate body detector

Abstract

The subject oscillation frequency generating section generates a subject oscillation frequency in response to the capacitance of subject when the subject contacts the measurement electrode. The subject recognition signal generating section generates a subject recognition signal corresponding to the subject oscillation frequency. The reference signal setting section previously sets a reference signal used to determine whether the subject is an animate body. The animate body detection control section compares the subject recognition signal and the reference signal to determine whether the subject is an animate body.

What is claimed is: 
     
       1. An animate body detector for determining whether a subject to be checked is an animate body, comprising: a measurement electrode contacting said subject;   an oscillation frequency generating section for generating an oscillation frequency in response to the capacitance of said subject when said subject contacts the measurement electrodes;   said oscillation frequency generating section consisting of: a first Schmidt inverter and a second Schmidt inverter connected in series, a first resistor connected between the input and the output of said second inverter through said electrodes, a second resistor connected between the input and output of said second inverter through said first resistor;     a subject recognition signal generating section for generating a subject recognition signal in response to said oscillation frequency;   a reference signal setting section for setting a reference signal; and   an animate body detection control section for comparing said subject recognition signal and said reference signal to determine whether said subject is said animate body.   
     
     
       2. An animate body detector as claimed in claim 1, wherein said subject oscillation frequency generating section comprises a CR oscillator. 
     
     
       3. An animate body detector as claimed in claim 1, wherein said subject recognition signal generating section eliminates the radio-frequency components of said subject oscillation frequency to generate said subject recognition signal, and said reference signal setting section sets an oscillation frequency corresponding to the capacitance of an insulation as said reference signal. 
     
     
       4. An animate body detector as claimed in claim 3, wherein said animate body detection control section determines that said subject is said animate body when said subject recognition signal is lower in frequency than said reference signal. 
     
     
       5. An animate body detector as claimed in claim 1, wherein said subject recognition signal generating section, as said subject recognition signal, sets a count value resulting from counting the duration of output pulse of said subject oscillation frequency, while said reference signal setting section, as said reference signal, sets a lower-limit count value recognizable as a count value resulting from counting the duration of output pulse of an oscillation frequency corresponding to the capacitance of said animate body. 
     
     
       6. An animate body detector as claimed in claim 5, wherein said animate body detection control section determines that said subject is said animate body when said subject recognition signal has a larger count value than said reference signal. 
     
     
       7. An animate body detector as claimed in claim 1, wherein said subject recognition signal generating section, as said subject recognition signal, sets the change rate of a subject oscillation frequency corresponding to capacitance exhibited when said subject contacts said measurement electrode for a predetermined period of time, while said reference signal setting section, as said reference signal, sets a lower-limit change rate recognizable as the change rate of an oscillation frequency corresponding to capacitance exhibited when said animate body contacts said measurement electrode for a predetermined period of time. 
     
     
       8. An animate body detector as claimed in claim 7, wherein said animate body detection control section determines that said subject is said animate body when said subject recognition signal has a larger change rate than said reference signal. 
     
     
       9. An animate body detector for determining whether a subject to be checked is an animate body, comprising: a plurality of sensors contacting said subject;   a time series change measuring section for measuring time series changes of information obtained from individual said sensors; and   an animate body detection processing section for determining that said subject is said animate body when said time series changes have a predetermined value or greater and said information obtained from individual said sensors are respectively different.   
     
     
       10. An animate body detector as claimed in claim 9, wherein said sensors react to a state of said subject, said state being electrical resistance, capacitance, moisture, or pressure. 
     
     
       11. An animate body detector for determining whether a subject to be checked is an animate body, comprising: a detection electrode contacting said subject;   a subject recognition change rate generating section for generating a subject recognition change rate in response to capacitance change when said subject comes close to said detection electrode; and   an animate body detecting section for determining whether said subject is said animate body, based on said subject recognition change rate.   
     
     
       12. An animate body detector as claimed in claim 11, wherein said detection electrode is coated with a thin film. 
     
     
       13. An animate body detector as claimed in claim 11, wherein said subject recognition change rate generating section applies a radio-frequency voltage to said detection electrode and generates said subject recognition change rate as the oscillation amplitude change rate or frequency change rate of said radio-frequency voltage. 
     
     
       14. An animate body detector as claimed in claim 11, wherein said subject recognition change rate generating section comprises a bridge type capacitance detecting circuit and generates said subject recognition change rate as a voltage change rate. 
     
     
       15. An animate body detector for determining whether a subject which exhibits a capacitance is an animate body, comprising: a plurality of measurement electrodes contacting said subject;   a basic clock;   a pulse oscillation circuit for generating a subject oscillation frequency in response to the capacitance of said subject when said subject contacts the measurement electrodes;   an edge detection circuit for carrying out edge detection of said oscillation frequency under control of an edge detection start signal;   a counter for counting a basic clock signal upon receiving a rising or falling detection signal from the edge detection circuit;   a change rate arithmetic circuit for receiving an input from said counter and calculating a time-based change rate of the input from the counter; and   a comparator for comparing said time-based change rate to a reference threshold value recognized as an animate body to determine whether said subject is said animate body.